Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Qual é a porcentagem total dos que têm n/a entre os de $40-50 mil?
 ###Tabelas: CREATE TABLE highest_innings (highest_innings_id AUTO_INCREMENT PRIMARY KEY, Rank INT, Score VARCHAR, Overs INT, Run Rate INT, Innings INT, Date VARCHAR, Test No. INT, Report VARCHAR) CREATE TABLE structures_past_or_present_between_550_and_600_m_1804_ft_and_1969_ft (structures_past_or_present_between_550_and_600_m_1804_ft_and_1969_ft_id AUTO_INCREMENT PRIMARY KEY, Pinnacle height VARCHAR, Year INT, Structure type VARCHAR, Main use VARCHAR, Country VARCHAR, Town VARCHAR) CREATE TABLE greatest_hits___best_of___compilations (greatest_hits___best_of___compilations_id AUTO_INCREMENT PRIMARY KEY, Title VARCHAR, Label VARCHAR, Year of Release INT, Country of Release VARCHAR, Peaches: VARCHAR) CREATE TABLE available_processors (available_processors_id AUTO_INCREMENT PRIMARY KEY, Series ^ VARCHAR, Model VARCHAR, CPU clock ( MHz ) VARCHAR, CPU cores INT, TDP ( W ) VARCHAR, L2 cache (KiB) VARCHAR, Radeon cores INT, DDR3 speed INT) CREATE TABLE faculty_and_staff (faculty_and_staff_id AUTO_INCREMENT PRIMARY KEY, Data VARCHAR, Headcount INT, Percent of total VARCHAR, Less than $25,000 VARCHAR, $25,000 to $40,000 VARCHAR, $40,000 to $50,000 VARCHAR, $50,000 to $60,000 VARCHAR, $60,000 to $70,000 VARCHAR, $70,000 to $80,000 VARCHAR, More than $80,000 VARCHAR, Mean VARCHAR)  
SELECT Percent of total FROM faculty_and_staff WHERE $40,000 to $50,000 = n/a